PRODH and lactic acidosis: However, lactate at concentrations commonly observed in both genetic and acquired lactic acidosis inhibits proline oxidase,27 the first enzyme of the proline (Pro) degradation pathway, with the rate of Pro degradation varying inversely with increased lactate concentration (ie, the Km of proline oxidase for Pro increases with increasing concentrations of lactate, with 5 mM lactate inhibiting ~75% of proline oxidase activity in rat liver mitochondria).27